*Basic

A UML sequence diagram shows how a set of objects interact in a process over time. It shows the messages that pass between participants and objects in the system, and the order in which they occur.[1]

**Intermediate

From the many diagrams proposed by UML, class diagrams and sequence diagrams are still widely used.[2] A sequence diagram is a type of interaction diagram because it describes how, and in what order, a group of objects work together. These diagrams are used by software developers and business professionals to understand requirements for a new system or to document an existing process.[3] Below is a sample sequence diagram:[4]

***Advanced

Sequence diagrams are used to model and visualize the logic behnd a sophisticated function, operation or procedure. They are also used to show details of UML use case diagrams. They visualize how messages and tasks move between objects and components in a system.[5]

Sources

[1] Editors. UML Sequence Diagram. Lucid. Lucidchart.com
[2] Editors. Which UML diagrams are still being widely used? Software Engineering. Softwareengineering.stackexchange.com
[3] Editors. What is a sequence diagram in UML? Lucid. Lucidchart.com
[4] Tanaka, E. Drawing a UML Sequence Diagram. Emitanaka.com
[5] Editors (2018) UML Sequence Diagrams. Geeks for Geeks. Geeksforgeeks.org